Ok guys. I bought my first boat recently and when I bought the boat the gentleman said to mix 50:1 for gas/oil. However, on the side of the motor it stats 100:1 and so does the book. Now, to me I should use the 100:1 as the book and motor states.

What year motor.? Older motors had diff mix ratios. As oil was different many yrs ago. For example I had an old 78 I think. 28 hp that said 32:1 mix. But with the advancement in oils the mix is now 50:1 today.

I have an `85 Evinrude, 25 horse, that was supposed to be a 100/1 mix, after the first two tanks (50/1). I was on my 3rd or 4th tank at 100/1 and it was knocking some. I asked my mechanic about it and he said to go back to 50/1 and stay there. Around ` `88 or later, OMC came out and said "OOPS, we shouldn't have gone so lean. Never mind. Go to 50/1." No new manual, no help if you had messed up your motor, just a letter. Luckily, I must have caught it on time. That may be the case with your yammy, too. Call or email the company. They may tell you to go stronger, or maybe not. Sometimes a company will NEVER admit an error, so I'd call an outboard mechanic and ask them, too. If you don't know a good outboard mechanic, check with several. Why more than one? Well, in over 30 years of using and beating up outboards on a daily basis, I've found that there are a few individuals that call themselves outboard mechanics that couldn't find their butts with both hands.

the manuel that came with the motor said 50-1 for break in and 100-1 after that like i said i have the # if you want to call but have the model # and serial # when you call the guy at yam. looked it up when i called . leave nothing to chance there is a lot of know it alls out there , you are the one paying the repair bills. some will give you advise and it is up to you to get the right answer, i hope this helps ,and nothing bad to others. and manuals can be pulled up on line